Allergenic α-methylene-γ-butyrolactones. A one-carbon degradation of isoalantolactone via Pummerer rearrangement of sulfoxides

Abstract

Isoalantolactone and α-methylene-γ-butyrolactone were separately treated with NaSPh, transformed into sulfoxides, and rearranged under Pummerer conditions (Ac₂O + (CF₃CO)₂O). The Pummerer products were hydrolyzed, oxidized, and decarboxylated resulting in the formation of 13-norisoalantolactone (with migration of the exo-C(4) double bond into position C(4)—C(5)) on the one hand and of γ-butyrolactone on the other. The isomeric norisoalantolactone 17 is a starting material for the synthesis of ¹⁴C-labelled alantolactone, 18.